WASHINGTON, March 25 (AFP) Mar 25, 2010China has stepped up pressure on North Korea to abandon its nuclear program, the US military commander for Asia said Thursday, playing down charges in Washington that Beijing could do more.

Admiral Robert Willard, head of the US Pacific Command, renewed calls on North Korea to return to six-nation talks on ending its nuclear program.

"We're convinced that the Chinese are committed to the denuclearization of North Korea, as we are," Willard told the House Armed Services Committee.

"They have made efforts -- increasing efforts, I think -- over the past year to exert their influence over North Korea," he said.

"At the end of the day, the choice to re-enter into six-party talks or not has been a North Korean refusal," he said.

China is reclusive North Korea's closest ally. Some US analysts say China's interests diverge from the United States as Beijing's main concerns are preventing refugees and maintaining a buffer state from US-allied South Korea.

Representative Mike Coffman, a Republican from Colorado, told Willard that Chinese leaders "certainly have the capacity" to put more pressure on North Korea.

"It would seem to me that they feel that they benefit by having an uncertain security situation in North Korea and by forcing us to provide our assets in that direction," Coffman said.

North Korea, which has tested two nuclear bombs, said last year it would return to the six-nation denuclearization talks that comprise China, Japan, the two Koreas, Russia and the United States.

But Pyongyang has since called for separate negotiations first with the United States on reaching a treaty to formally end the 1950-53 Korean War.